Not related to Firefox, but here is a an answer, http://www.whatsmyip.org/

It is highly likely that you have viruses on your machine, so please do the following:

• Update your plugins at https://www.mozilla.org/plugincheck/
• Scan for Malware, Troubleshoot Firefox issues caused by malware
• Update to Windows 8.1, install all other updates Microsoft gives you
• Run Windows Defender regularly

Try to clear the cache and cookies from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"